Question

What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases.
(ii) The temperature of the solution decreases.
(iii) The temperature of the solution remains the same.
(iv) Salt formation takes place.

• A. (i) only
• B. (i) and (iii)
• C. (ii) and (iii)
• D. (i) and (iv)

Hint:

Every neutralization reaction between a strong acid and a strong base releases a fixed amount of heat energy, approximately \(57.3\text{ kJ/mol}\).
This exothermic nature always causes the temperature of the reaction vessel to rise.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks us to identify the correct physical and chemical changes that occur when an acidic solution is mixed with a basic solution in a test tube.

Step 2: Key Formula or Approach:
The reaction between an acid and a base is called a neutralization reaction. The generalized chemical equation is:
\[ \text{Acid} + \text{Base} \to \text{Salt} + \text{Water} + \text{Heat} \]

Step 3: Detailed Explanation:

• When an acid and a base are mixed together, they react chemically to neutralize each other's properties.

• The hydrogen ions (\(H^+\)) from the acid react with the hydroxide ions (\(OH^-\)) from the base to form water molecules:
\[ H^+\text{(aq)} + OH^-\text{(aq)} \to H_2O\text{(l)} \]

• The remaining ions from the acid and base combine to form an ionic compound known as a salt. Thus, statement (iv) "Salt formation takes place" is correct.

• Neutralization reactions are highly exothermic in nature.

• During this reaction, a significant amount of heat energy is released into the solution. This released thermal energy increases the kinetic energy of the water molecules, causing the overall temperature of the mixture in the test tube to rise.

• Thus, statement (i) "The temperature of the solution increases" is also correct.

• Combining these two accurate observations, statements (i) and (iv) describe the complete physical and chemical characteristics of the process.


Step 4: Final Answer:
The correct options are (i) and (iv), which corresponds to Option (D).